In general, a processing apparatus using a focused ion beam uses its micro-processing capability for milling and thin-film accumulation in a gas atmosphere and its high positioning accuracy to carry out, for instance, failure diagnosis or correction of an integrated circuit, repair of photo mask defect, preparation of a sample of a cross-section of a semiconductor device for a transmission electron microscope (TEM), processing of a magnetic head using a magnetic resistance (MR) effect, or processing of a micro electro mechanical system (MEMS).
Since processing by the focused ion beam apparatus requires a long time in many cases, and high-accuracy processing is required, detection of drift amount in the course of processing and reduction of influence of the drift by fine-adjustment of an ion beam irradiation area with the drift taken into account has been performed. In order to find the drift amount with high degree of accuracy, a method including steps of: forming in advance a minute hole with the ion beam at a position of the sample other than the area to be processed; obtaining a secondary electron image of the area including the minute hole or a secondary ion image of the types of atoms included in the base film, to find the position of the minute hole in advance; starting the processing; obtaining again the secondary electron image of the area including the minute hole formed in the course of the processing or the secondary ion image of the types of atoms included in the base film; finding the shifted amount of the position of the minute hole; and fine-adjusting the ion beam irradiating area, is performed.
For example, in the case of a photo mask defect repairing apparatus, a minute hole is formed on a light-shielding film on a glass substrate at a position other than the area to be processed in advance by the ion beam, the area including the minute hole is scanned before processing, the position of the minute hole is detected from the secondary ion image of Si included in the glass substrate, and the position is registered. Subsequently, the processing of the defect area is started, then the processing is interrupted once in mid process for scanning the area including the formed minute hole again to find the current position of the minute hole from the secondary ion image of Si included in the glass substrate, fine-adjustment of the ion beam irradiation area is performed based on the difference from the registered position which is the drift amount, the processing is started again, and the registration of the current position of the hole is updated. Improvement of the processing accuracy is achieved by repeating calculation of the drift from detection of the position of the hole and comparison with the registered position, fine-adjustment of the ion beam irradiation area, and starting the processing again (for example, see JP-A-63-305358 (P. 3-4, FIG. 1)).
When correcting the drift amount in the image of the secondary ions included in the base substrate, if the amount of incident ions injected is too small, or the minute hole is too small, FIB-CVD source gas or gas for gas assist etching is adsorbed in the hole formed by the ion beam and hence the secondary ion image may become invisible. Therefore, the size of the hole must be increased. However, when the size of the hole is increased, accuracy of the drift correction is lowered. Also, when the size of the hole is increased, if an object to be repaired is the photo mask, the hole formed for the drift correction may also be transferred to the circuit.
When the photo mask is repaired using the photo mask defect repairing apparatus, if the size of the hole formed for the drift correction is too large, the hole formed for the drift correction is filled up with the FIB-CIV film after the processing is completed. However, depending on the shielding film patterns, there are cases in which the film is not adhered because the primary beam consists of Ga and instead further etching is done, whereby it becomes easier for the hole to be transferred, or even if the hole is filled up, another defect is generated on the glass substrate around the hole due to the halo caused by the tail component of the beam.
When scanning an area of the light-shielding film including the minute hole formed at a position other than the area to be processed on the glass substrate by the ion beam in advance, secondary ion signals of the same atoms as the ion beam injected into the substrate are detected, not the secondary ion signals of the atoms included in the base film, and the position of the hole is stored. Then, during the processing, the area including the hole formed is scanned and the secondary ion signals of the same atom as the incident ion are again detected to detect the position of the hole, the position of the hole previously detected and the current position of the hole are compared to obtain the amount of shift of the position of the hole, and with this shifted amount regarded as the drift amount, the processing is started again in the irradiation area which offsets the drift amount.
Since the secondary ion of the same atomic species as the incident ion beam is detected when determining the position of the hole, there is no possibility that the secondary ion can be difficult to detect due to the injection of the incident ion and hence the secondary ion image is difficult to see as in the conventional art. In addition, when the hole is minute, even though FIB-CVD source gas or gas for gas assist etching is adsorbed to the hole, the intensity of the secondary ion detected at the hole increases because the hole has been injected with the incident ion every time when the area including the hole is scanned, and hence even the minute hole can be detected more easily than in the conventional art, and hence the drift can be corrected with high degree of accuracy. Further, when the ion source is gallium (Ga), there is the advantage that gas is not readily adsorbed to a surface layer in which gallium is injected.
When repairing the photo mask by the photo mask defect repairing apparatus, since the drift is corrected by a minute hole which is as small as a half of the wavelength of a reduced projection exposure apparatus, the hole formed for detecting the drift amount is not transferred. Since it is not necessary to fill up the hole, the problem caused by filing the hole as described above does not occur.